A subtle insight into nano-convergence of substrate thickness in melt-grown single-co-crystals

Poly(lactic acid)-based materials with enhanced gas permeability for modified atmosphere packaging of Chinese bayberry

Biodegradable plastics are increasingly utilized in packaging, driven by green chemistry and environmental responsibility. Among them, poly(L-lactic acid) (PLLA) stands out due to its biodegradability and biocompatibility. However, its limited gas permeability and selectivity hinder its application in produce preservation. To address this, polyethylene glycol (PEG), which enhances CO2 selectivity, and polydimethylsiloxane (PDMS), known for its large free volume and high gas diffusion coefficients, were incorporated into PLLA to synthesize two triblock copolymers, PL-E-LA and PL-D-LA. Films with varying block ratios were prepared via solution casting. The results showed that elongation at break for PL-E-LA and PL-D-LA increased by 2.5-fold and 8.7-fold, respectively, while their crystallization temperatures (Tcc) decreased to 79.4 °C and 108.3 °C. Scanning electron microscopy (SEM) revealed spherical phase separation in PL-D-LA and finger-like structures in PL-E-LA. By blending these copolymers, gas permeability and the CO2/O2 permeability ratio were optimized. At 5 °C, the CO2/O2 permeability ratio of PL(D25/E75)LA films reached 9.1, meeting the ideal range (8-10:1) for fresh produce packaging. Atomic force microscopy (AFM) confirmed the PL(D25/E75)LA film exhibited the lowest surface height (52 nm) and roughness (Ra = 4.051), with a fine, uniform phase separation that facilitated gas diffusion and optimized permeability. The application of PL(D25/E75)LA to Chinese bayberry preservation effectively reduced weight loss, delayed firmness degradation, and maintained quality attributes such as color, sugar, and acid content, demonstrating its superior preservation performance. This study highlights the potential of PLLA-based packaging materials with optimized phase separation for produce storage and transportation.